Virginmedia's limit is 20MB for attachments, taken from their help pages ... "You can send and receive e-mails with attachments of up to 20MB in size. Note that your contacts may be using e-mail systems that can't handle such large message sizes, so keep this in mind when sending attachments
If someone tries to send you a message larger than 20MB, the message will be returned to the sender." You only get 7GB total storage so not likely to have 25GB attachments